Two U.S. agencies closely involved with GPS are calling on the FCC to force a more complete study of potential interference with the navigation system from the planned LightSquared mobile broadband network.

In a March 25 letter to U.S. Federal Communications Commission Chairman Julius Genachowski, deputy secretaries from the Department of Defense and Department of Transportation voiced concerns about the FCC's process for granting a waiver to LightSquared. Aviation news site Flightglobal reported on the letter on Monday. LightSquared plans to launch a national LTE (Long Term Evolution) network later this year with a satellite network to further extend its reach. The company plans to sell its services through wholesale partners that would include Best Buy and Leap Wireless carrier Cricket.

The DOD and DOT were not sufficiently involved in the development of the work plan for testing LightSquared's network, the agencies told Genachowski in their letter. Calling themselves "the national stewards and global providers" of GPS, the departments said they needed to be actively engaged with the process.

Another problem with the plan for evaluating interference is that there is no requirement for consensus among the various participants, the letter said. "DOD and DOT need to understand how differing conclusions and recommendations developed during the ... process that could affect national security and transportation safety will be addressed," said the letter, which was signed by Deputy Transportation Secretary John Porcari and Deputy Defense Secretary William Lynn.

"Finally, DOD and DOT strongly advise that a comprehensive study of all the potential interference to GPS is needed," the letter said.

Members of the GPS community have told the FCC that they are satisfied with the LightSquared review process so far, FCC spokesman Robert Kenny said in an e-mail message on Wednesday.

"LightSquared will not be permitted to move forward with service under the waiver until potential interference issues are addressed," Kenny said.

LightSquared said it was sensitive to concerns about interference and would not launch its network until the review was completed to the FCC's satisfaction.

"As part of this effort, we are cooperating with federal agencies, the GPS community and GPS engineers in a transparent and technically accurate testing program to address issues relating to GPS receivers," Executive Vice President for Regulatory Affairs Jeff Carlisle said in a prepared statement. "We are also providing equipment and personnel to the U.S. Air Force's Space Command, NASA and other federal agencies to help them begin their own testing processes."